Over a period of three years (December 1980 through November 1983) the incidence and epidemiological features of acute rheumatic fever (ARF) and acute poststreptococcal glomerulonephritis (AGN) were studied prospectively in two regional hospitals in Kuwait serving a childhood population of 225,000. The study included 146 children with ARF and 256 family members and 125 children with AGN and 199 family members. The annual incidence of ARF and AGN were 19.6 and 17.8 respectively per 100,000 childhood population (7.3 and 6.7 respectively per 100,000 total population). Both diseases occurred sporadically throughout the year with a similar peak in winter. The clinical profile of ARF was essentially similar to that reported from temperate climates, and AGN followed mainly throat infections. Microscopic haematuria was detected in ten ARF family members (4%) and in 20 AGN family members (10%). Haematuria and low C3 were found in two (0.8%) and in seven (3.5%) ARF and AGN family members respectively. Of the nine family members with subclinical nephritis the group C streptococcus was isolated from three (33%). The geometric mean titre (GMT) of antistreptolysin O (ASO) and of antihyaluronidase (AH) in ARF and AGN patients were markedly elevated. Although the median age of ARF and AGN family members were 13 and 15 years respectively, yet the GMT of ASO and AH in the family members were slightly higher than those of the normal childhood population.